1. Technical Field
The invention relates to a battery unit for hybrid or electric vehicles, comprising a cell module and a cooling device.
2. Discussion
Modern hybrid or electric vehicles use accumulators for storing electric energy. Such accumulators usually comprise a battery of single cells placed in a common casing. During charging and discharging of such accumulators heat losses arise within the single storage cells. It is important for the capacity and life of the storage cells that the lost heat is removed from the storage cells such that the battery is operated within the limits of a defined temperature range. In addition, the temperature spread must not become too wide, over the single cell and over the whole battery as well.
Natural heat dissipation through convection or radiation to the environment cannot meet the requirement of homogeneity due to the high cell density within the battery and the enclosing casing. Furthermore, certain maximum operating temperatures of the cells must not be exceeded over longer periods of time. During warm weather, therefore, it may be necessary to dissipate the heat to maintain a temperature level below the ambient temperature. In order to meet the requirements the storage cells impose upon the temperature level and distribution, electric accumulators for hybrid or electric vehicles require active cooling devices. While some prior art already offers cooling bodies as an integral component of a storage battery unit, some issues still exist.
Storage cells are increasingly being developed that geometrically do not correspond to the conventional cylindrical design but instead utilize a prismatic design. Prismatic cells, due to the stack-like arrangement of the cells, enable utilization of the space in the battery casing more efficiently than cylindrical cells. On the other hand, prismatic cells frequently require strong pressure against two of the large surfaces in the direction parallel to thickness. An appropriate clamping device per module to provide appropriate pressure to a combination of at least two cells to build a unit, or of whole batteries, can collide with the space for installing the cooling device, and hence must be considered during design. While these specifics do not make it impossible to adapt cooling devices known as being suitable for cylindrical cells, often the specific advantage of a volume efficient cell arrangement offered by prismatic cells cannot be utilized due to the required cooling.
From DE 10 2004 005 393 A1 (U.S. Publication No. 2005/0170240), an electrochemical energy store is known that is equipped with heat exchanger units and several electrochemical storage cells located between the heat exchanger units. This energy store is based on the principle of a plate heat exchanger. Layers of storage cells and cooled plate elements are alternatingly displaced in a stack. Here, the plate elements that are passed by a coolant consist of several parallel displaced flat tubes that are deformed to form waves corresponding to the cylindrical contour of the cells. FIG. 12 of DE 10 2004 005 393 A1 (U.S. Publication No. 2005/0170240) shows a stack of two cooling plates and two planes of cylindrical storage cells. The heat of the cells is dissipated over almost the total shell surface.
DE 10 2006 010 063 A1 proposes a socket mount for several cylindrical storage cells that is passed by a coolant. The root ends of the cells are inserted into a mount so that the heat is dissipated over the lower face and a narrow lower portion of the shell surface.
In case of stack design with prismatic cells, the increased clamping pressure required for prismatic cells in stack direction may cause damage to the cooling elements designed as flat tubes or plates. In case of socket mount with prismatic cells, a gap-like space is present between the cells of a module. With prismatic cells, the gaps would have to be filled with additional material in order to prevent bending, hence destruction of cells and/or the socket during pressing the cell modules. Often the battery subassemblies, the cell module and the cooling device, cannot be separately manufactured or finished. That makes the manufacture of the batteries more complex, involving risks during functional checks, particularly if the tightness of the cooling device, for example, can only be checked with the battery completely mounted.
U.S. Pat. No. 6,858,344 describes a battery stack including a number of prismatic batteries displaced in a parallel and integral bundle. Each prismatic battery includes an group of electrode plates and an electrolyte accommodated in a prismatic battery casing. A metal plate is integrated with the side wall of the prismatic battery the metal plate arranged parallel to the electrode plate group. A heat transition region projecting above the prismatic battery casing is provided on at least one side of the metal plate. A heat exchanger is provided such that a heat exchanger surface of the heat exchanger is brought into contact with the heat transition region projecting above the prismatic battery casing of the prismatic battery. After then, the battery stack and the heat exchanger are fastened. The heat exchanger is fastened using two mounting plates, which also serve to hold the battery stack together. For that a couple of projections project from either of both lower ends of a prismatic cell. In the cell stack projections of one of the lower ends of the stacked cells are fixed with screws using a mounting plate. A second mounting plate fixes the projections of each other ends of the cells. As a result the prismatic cells are tightly fastened and joined together as a battery stack. At the same time, the mounting plates serve as carrier device for the heat exchanger.
In DE 10 2007 063 176 A1, a battery with a heat conducting plate for tempering the battery is described, wherein the heat conducting plate is provided with several single cells parallel and/or serial switched together that are connected heat conducting to the heat conducting plate which in the range of poles of the single cells is provided with recesses through which the poles of the single cells project. The heat conducting plate is provided with a number of recesses corresponding to the number of poles, or pole couples, whereby a filling opening for the electrolyte is integrated into at least one of the poles of each single cell.
In DE 10 2008 016 936 A1, an electrochemical energy storage unit is disclosed that comprises a plurality of flat cells. The plurality of flat cells are displaced one above the other in a stack with their flat sides essentially arranged parallel to each other. At least one metal cooling sheet is located between two adjacent flat cells that is bent off at least one side. Further, a heat sink is provided as cooler to which the at least one metal cooling sheet thermally contacts. The heat sink is provided with recesses. The heat sink includes flat tubes that are passed by a refrigerant or coolant, or another fluid, whereby the recesses are provided for accepting the pins of a plastic rail, which subsequently can be formed to rivet heads such that a form closure is created. The plastic rail is attached to the respective metal cooling sheet by clipping, gluing or overmolding. For increased stability the pins may be guided in reinforcing members.